Semi-automatic telephone trunking system.



T. G. MARTIN.

SEMI-AUTOMATIC TELEPHONE TRUNKING SYSTEM.

APPLICATION man SEPT. 13. 1901. HENEwED MAY 2s, |917.

Patented J an. 15, 1918.

2 SHEETS-SHEET .T. G. MARTIN. SEMI-AUTOMATIC TELEPHONE TRUNKING SYSTEM.

APPLlc/mon FILED SEPT. I3. |901. -nenzwfu MAY 2s`..1|1.

Patented. Jan 15, 1918. 2 SHEETS-SHEET 2.

to communicate with l UNITED lsTATns PATENT onirica.

l'rnniao'r e. MARTIN, or cHIcaeo, ILLINOIS, Assmann, BY Masini ASSIGNMENTS, To

AUTOMAIIC ELECTRIC C0., A CORPHATION Ol' ILLINOIS.

Specification of Letters patent.

Patented Jan. 15, 1918.

Application illed September 13, 1907, Serial No. 392,686. Renewed lay 28, 1917. Serial No. 171,570.'

To all 'whom it may concern.'

Be it known that I, TALno'r G. MARTIN, a citizen of the United States of America,

"and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Semi-Automatic Telephone Trunking Shystems, of which the following is a 'speci cation.

My invention relatesto telephone systems in general, but more particularly to systems v in which both automatic and manual switchboard apparatus is employed for connecting calling subscribers with called subscribers, such systems being' ordinarily known as semi-automatic systems.

The principal object of my invention is the provision of an arrangement for enabling the subscribers of a private eigchange the subscribers of a main exchange, in a system of that character in which the subscribers at the private exchange areboth manual. and automatic, and in which the'main exchange is provided with automatic apparatus for the automatic subscribers, as hereinafter set forth; the rovision of` an improved two-way trunk ine, and a manual switchboard operators cord circuit,`having suitable supervisorl apparatus for enablin the operator to fu ly supervise an `and a l connections made through the me ium of said trunk line and cord cir,- cuit, whether between automatic subscribers,

, or-between automatic and'manual subscribers, according to the character of the call; 'and the provision of certain details and features of improvement and combinations neral eiiiciencyand serviceabil-ity of asemi-automatic trunking system of' this particular character.

To the foregoing and other useful ends,

Y my invention consists in matters hereinafter set forth and claimed. y t

4Figure 1 Vis la diagram of a combined manual and automatic private `branch exchange telephone system embodying the,

principles of my invention, a cou le of manual `substations being shown at and A' and an automatic substation at D. The manual substations A and A are each connected with lines which terminate in the jacks C and C', respectively, of the private branch, and the automatic substation is y shown vconnected with a line which terminates in the jack C2'. The trunk'circuit E,, which is adapted to;` connect with the Jacks C, C and C, is used by the operator to connect any substation of the private branch exchange with an outgoing trunk line to the main centralexchange, and is also used by incalling subscribers. Therefore the cord E is a two-way cord; and the cord F is used to connect any two local substations-tliat is, any, two substations having their lines terminating in the private branch board, such as A and D for instance. The central battery B is shown having its ositive terminal preferably rounded at Fig. 2 shows diagrammatic-ally the switching apparatus of an automatic central oiiice in connection` with which I have elected to explain my invention. At H is shown a first-selector switchallotted to the trunk line leading to the private branch board shown in Fig;J 1, said trunk line terminating in the cord" At I a connector switch is shown, and the selector switch H is allotted to the line #220 that leads to the substation D', which station belongs to this main automatic exchange. At K and L are represented a ringing generator and busy-signaling machine, respectivel The battery of the automatic centralv o ce is shown at B and has its positive terminal preferably grounded at G'. y

Figs. 1 and 2' taken together show the switching mechanism involved when the substation D, which is a substation of the private branch board', calls the station D',

Vwhen the receiver lis removed, is adapted to engage the contact point 4, whereby the transmitter 5 in series with the receiver 2 becomes bridged across the line. When the receiver 2 is restored to the switch-hook the primary circuit through the transmitter and receiver is broken, leavin the ringer 6 in series with thel condenser 7 the allotted'linc. The substation -D, like the substation D', comprises the usual receiver aan@ the switclrfhook 9, which inamhas a noI ridged across v scriber controls the release number of cam arms 10, 11, 12 and 13. When the switch-hook is up the cam arm 10 closes the springs 14 and 15 in contact, whereby the primary windin 16 of the induction-coil 17 in Series with t e transmitter 18 becomes bridged across the substation line. Also, when the switch-hook is up the cam arm 11 permits the springs 19 and 20 to engage, whereby the substation becomes connected with the substation ground G2. When the switch-hook is down the cam arm 12 presses the springs 21 and 22 into engagement, bridglng across the line the ringer 23 in series wlth the condenser 24. The si aling device comprises' a push-button sprlng 25 which normally rests in Contact with the spring 26, but which when pressed en ages the contact point 27. The calling evice comprises the push-buttons 28 and 29, and the springs 30 and 31 which normally rest in engagement. with the contact points 32 and 33; but when the buttons 28 and 29 are pressed, the said s rings then engage the ground contact 34. e means whereby the subscriber may release the central office switches comprises the springs 35, 36 and 37, known as the .release springs. When the receiver is restored to the switch-hook said release springs are pressed into engagement momentarily by the cam arm 13.

The first-selector switch shown at H may be of any suitable or approved type, for example of the type described in vUnited States Patent No. 815,321, granted March 13, 1906, to Keith,.Erickson and Erickson. In this switch the switch shaft (not shown) carries the .vertical and rotary wipers 38 and 39, respectively, and the private wiper 40. The side switch is well known and comprises the side switch wipers 41, 42, 43 and 44. The side switch is under the control of the rivate magnet 45, and in their normal or rst position the wipers 41, 42, 43 and 44 occupy the contact points 46, 47, 48 and 49, respectively. In the second position they rest on the contact points 50, 51, 52 and 53, respectively, and 1n. the third position the contact points 54,55, 56 and 57 are engaged by their respective wipers. rljhrough the medium of thel vertical line relay 58, and while the sideswitch is in first position, the subscriber controls the vertical ma et 59, whichlatter operates to raise the switch shaft and wipers 38, By means of the rotary line relay 60, and while the side switch is'in first position, the subscriber controls the private ma et 45 and, therefore, the side switch. Wlile the side switch is in second position the rotary magnet 61, which opera-tes to carry the switch shaft and wipers 38, rotary direction, is energized. The vertical and rotary line relays 58 and. 60, acting conjointly, provide means whereby the Submagnet 62 while 76 and 77.

39 and`40 vertically.

39 and'40 in a first or second position. asses to the third position eetor H is of the trunkthe side switch `is in I f the side switch then (since the se release type) the selector H is controlled.

through the ynext switch, with which latter a connection is then established, and through the private wiper 40 and by means of ,the back-release rela 63. The bridge-cut-oii' relay 64 is proviri'ed toA open the connection between theline relays 58 and 60 and lbetween said relays and battery B. This is desirable, because if the relays are not disconnected from each other and battery the ringing current for signaling the subscriber Y For example, the connector switch shaft (not shown) carries, like the selector, the line wipers 65 and 66 and the private wiper 67. The'connector switch is a so controlled by the calling subscriber through the medium of the vertical and rotar line relays 68 and V69. The vertical line relay 68 directly controls the vertical magnet 70 andy also the rotary magnet 71. The function of the vertical magnet 70- is to give the shaft and shaft wipers a vertical motion,l and the rotary magnet 71 imparts to the shaft and shaft' wipers a rotary or circular motion.-

The rotary line relay 69 controls magnet 72, which latter, under certaln conditions, controls in turn the vertical and rotary magnets 70 and 71,/ release magnet 7 3 and also the Avside switch wipers 74, 75, p The side switch, like the side switch of the selector, has a normal or first position, a second position anda third posin. The release magnet 73 is alsol controlled by the vertical and rotary line relays 68 and 69 conjointl By the use of the condensers 78 and 79 t e connector divides the-talking circuit into two sections. The differential rela 80 controls the energizing circuit of the re ease magnet 73, and also of the back-bridge relay 81, which latter provides the called substation with battery current for talking' purposes, and which upon energizing closes a circuit that provides the calling substation with battery current for talking purposes. When the side switch is in third position the vertical line relay 68 controls the ringer relay 82 vby means of which .the ringer nerator K is bridged across the terminafs of the called line to the private lic into two sections.

` signal the called subscriber. When the shaft is raised the normal arm 83 permits the l thejacks C, C and C2. The relays 861and both ways over the trunk conductors 92 and,

93,4 which connect the main and sub ex `in normal position, the relay 99 87 provide means for suppl ing the substations with battery current or talking purposes. By the use of the signal lamps 88 and 89 the operator obtains supervision over the lines corresponding to the jacks in which the plugs lc and c are inserted. The condensers 90 and 91 divide the-talkingcircuit By means of the key f the operator may .bridge her talking set across the calling end of the cord circuit, and by means of the key f a signal may be sent out to the called line. The cord circuit E, as aforesaid, is adapted for making calls changes. The signaling lamp 94 indicates to the operator when the trunk line con-l ductors 92and 93 have been vseized by a calling subscriber at the main automatic exchange, and acts as a line signal from the trunk side. The lamps 95 and 96 are supervisory lamps, each acting as front and back supervisory lamps, depending upon the direction of the call. If the `call is from the branch exchange to the main oiiice the' lamp 96 acts as a ront and the lamp 95 as a back supervisory signal. Vice versa, if the call comes` from the main exchange, then the lamp 95. acts as a front and the lamp 96 as a back supervisory signal. By means of the key e the operator may bridge the generator 97l across the plug c2, and by throwing the key in the opposite direction the plug c2, as shown in Fig. 1, may be extended to the trunk conductors 92 and 93. In this way the subscribers A, A', D, etc., may be called or put in connection with the trunkV conductors 92 and 93 for calling urposes. B

means of the condensers 97 and 98 the trun circuit E is divided into two sections, as is ordinarily the custom. `Whenthe key eis rovides means for supplying the plug-.en `of the line `with battery current for talking urposes, and when the key e is operate as shown, (with the springs 164, 216, 151, 238, 219, etc., all shifted) the plug-end of the line receives talking current through the windings 'of the relays 100, 101 and 102. The relay 104, under certain conditions, controls the supervisory lamp 95 and the trunk signal lamp 94. By means of the-key e the operator may bridge her calling device d across theutrunkline conductors 92 and 93, and by operating the key in the opposite direction an operators set is bridged lacross the same trunk line. By means ofthe release relays 105 and 106 the trunk line conduc-` tors 92 and 93 may be grounded simultaneously to bring about the release of the central ofiice switching apparatus.

The operation of the cord circuit F may be better understood by considering its use for connectin one substation with another vsubstation, uppose, for example, that the subscriberat substation A desires to communi- Cate With the subscriber at substation A. When the calling subscriber removes the receiver 2 the switch-hook 3 engages the contact point 4, whereby an energizing circuit is established through the line relay 107. Said circuit extends from ground Gpthrough the springs 108 and 109, conductor .110, through the switch-hook 3, contact point 4, receiver v2, transmitter 5, conductor 111, springs 112 and 113, through the relay 107 to the battery lead 114, thence through battery.V -B and to ground G. The relay 107, upon energizing, draws its armature 115 onto the ycontact point 116, thus closing the circuit through f the line lamp 117. The circuit through the said lamp extends from groundy GF through the lamp 117, contact point 116, armature l11.3I to the battery lead 114, thence through battery Band to ground G. The operator, in response to the signal, inserts the plug c into the jack C, whereby the tip 118 and sleeve 119 of the plug c engage the tip and sleeve springs 112 and 109 and carry them out of engagement with the springs 113 and 108, respectively. .The circult through the line relay 107 being thus broken, said relay denergizes,andtlie armature 115 returns to normal position, whereby the circuit through ing current passes through the ringer 124 at substation A', The subscriber at substation A', upon removing the receiver 128 from the switch-hook, closes a circuit which'provides the transmit-ter 125 with battery current for talking purposes. This circuit extends from ground G through the winding 126 of therelay 87 to the springs 120 and 122, conductor 127 through the transmitter 125, receiver 128,

the receiver 2 is removed from the switchhook. Furthermore, whenthe plug c enters the jack C the ring 134 engages a -swers, asexplained, the relay 87 energizes and attracts the armature 136, whereby the circuit through the said lamp isbroken, and

` the operator knows that the called subscriber has answered. Similarly, the relay `86 attracts its armature 138 and breaks the circuit through the supervisory lamp 88. Now, when both subscribers restore their receivers to their switch-hooks, the energizing circuits through the relays 86 and 87 are destroyed. The armatures 138 and 136 again resume their normal positions, whereby the circuit through the supervisory lamps 88 an'd 89 is again established, thus giving the operator the disconnect signal. Suppose that the subscriber at vsubstation A had desired connection with substation D. In that case the plug c would have been inserted in the jack C2, and the subscriber at substation D called in the same manner. In\ a similar manner, when the receiver 8 is removed from the hook 9, a circuit is closed through the relay 87, and the. two 'substations A and D are connected in a manner similar to that explained. Of cou1se,should the subscriber atl substation D desire connection with substation A he removes his receiver, closes springs' 14 and 15 and up an energizing circuit through the signal relay 235". In that case, the pl-ugs c and of .wouldbe reversed-that is,y the plug c would "be inserted inthe jack C2 and the plug c would be inserted in the jack C. Suppose that the subscriber at A desired connection with the subscriber at D', which is a substation of the central exchange. fore, and, upon learning that substation D on the line#220 is wanted, removes the plug c from the jack C and substitutes the plug c* of the trunk circuit, whereby the substation A f becomes connected directly through the trunk line conductors 92 and 93. The'i'substation A being amanual subs'tation, the desired number may be called by the lo erator by means of the calling devicey d w ich is `represented by two push-'button springs 139 `and 140 and a ground post 141.. Thekey4 e is operated to separate the springs 142'and 143 'from engagement with the springs 144 and 145, and to carry the former into en- `Jgagement with the springs y,146 and 147.

The springs 148 and 149 also engage, but at .this tlme without effect. By the separation Vof the -said springs the operator disconnects the trunk conductors from the substation A, and by the engagementof theabove-ment'ioned springs the calling.devicedis'bridged across the trunk conductors 92 and 93. It

The operator then answers as be- .l

will be seen that at the instant that the plug c2 is inserted inthe jack C the substation A is provided with battery currentfor talk,- ing, purposes over the following i circuit:

from ground G5 at the cord circuit E 70 throughthe winding 150 of the relay 99 to the springs151 and 152, springs 153 and 154 to the sleeve 155 of the plug c2, sleeve spring 109 of the jack C to the conductor 110,

switch-hook 3, contact point 4, receiver 2,'75

relay 99 to the battery `lead, 114, thence ao through battery B and to ground G. ,The said relay 99 energizes. thereby moving the Varmatures 166 and 167 from Yengagement with the contact points 168 and 169, 'respectively. Also, when the ring 162 of the plug c? engages the ring 163 ofthe jack C, a circuit is closed through the release relay 105 in series with the release rela'y 106, and throu h the supervisory lamp 95. The circuit t rough the said relay extends from,

y ground G3 through the ring`163 and ring 162,. through the springs 164 and 165, through the relay -105,.thence through the relay 106 to the battery 114, thence through battery B and to ground G. baidv relays', upon energizing, attract their armatures 170 and 171 and 172 and 173. The relay 105v is a quick-acting relay, .while the relay 106 is a slow-acting relay, and hence the armatures 170 and 171 disengage from" the .contact points 174 and 175 before the armatures 172 and 173 of the relay 10G/engage the groundl post 176. The circuit`through the supera visory lamp 95 extends from ground -Gs` through the ring 163 of thejack C to the ring 162 of the plug c, through the springs '164 and 165, through the lamp 95 to the contact point 177, amature 178 tothe battery lead 114, thence through batteryB to ground G. This lam` continues to burn, until the called subscri er answers, at which time .the relay y104 becomes energized and operates to ybreak the circuit through the said lamp, as

willbe explained. To call the number 220 the operator pressesthe sprin 139 onto the ground POS y141 twice and tr e spring 140 onto the rou-nd post 141 once for the first digit. Li ewise,l for the second digit and for the third digit the spring 139 is pressed `a corresponding number of times and the spring 140 is pressed-once `each time.' By pressing the `springs 139 and 140 onto the ground post `141 a corresponding number of impulses are delivered to the vertical and rotary trunk conductors 92 and 93. Grounding the vertical .line conductor twice energizes the vertical line relayv 58 of the selector`H (Fig. 2) over a clrcuit extending from ground G to the ground post/141,

spring139, key springs 146 and 142 to the Vvertical trunk line conductor 92, to the side switch wiper 41, contact oint 46, vertical line relay 58, bridge-cut-o springs 179and 180 to the battery lead 181, thence through battery B to ground G. When the spring 4 140 engages the ground post 141, an enerrst digit the selector shaft wipers 38,39

and 40 rest in engagement with the trunkA line conductors leading to thel connector switch I. The second digit is called the same i as the first; but nthis time the ground im pulses are directed toward the vertical and rotary line relays 68 and 69 of the connector switch I. The connector line relay 68,` being energized twice, closes anenergizing circuit through the vertical magnet 70 twice, which magnet, in turn operates to carry the shaft wipers 65, 66 and 67 one step at a time until the said wipers are carried up two steps and raised to a bank level in which are located the terminals of the normal conductors 183, 184 and 185, the former two of which leadto the desired line. When the rotary line conductor 93 is grounded the connector rotary line relay 69 becomes energized, which in turn energizes the rivate `ma et 72, which flatter operates to re ease the si e switch from.

first to'second position. The last digit bein naught the operator grounds the vertica trunk conductor, 92, as previously described, wherebythe` vertical line relay 68 receives ten impulses and the rotary line relay 69 one. Whenv the vertical line relay energizes, it operates to close an energizing circuit through the rotary magnet 71 instead of throu h the .vertical magnet 70. Each time that t e rotary magnet is energized it operates to rotate the shaftwipers 65, 66 and 67 one step at a time until the said wipers are carried into engagement with the nor-` mal conductors 183, 184 and 185 that lead to the selector switch H in which are the ter-v minals of the desired line. The operation of the rotary line relay for the last digit completes an energizing circuit through the private magnet7 2, which latter now operates with one of two results, namely thefrelease o f the side switch from first -to second position, or the so-called busy-release of the connector. Su pose the former result to occur and the si e switch to pass to third position, thus extending the trunk conductors 92 and 93 to the normal conductors 183 and 184, re ectively. Furthermore, when the side switch passes tothird position a guarding its normal position.

. tor I energizes from switch shaft wiper 67, which latter engages the private contact of the called line. Also,

when the side switch wiper 77 engages the' third position contact point anenergizin circuit is closed through the bridge-cut-o relay` 186 of the selector H', thereby removing the bridge formed by the vertical and rotary linerelays 257 and 2580i the said selector.

To"signal the called subscriber the operav tor presses Vthe push-button spring 139 onto the ground post 141, thereby establishing an energizing circuit through the connector vertical line relay 68. It will be assumed that the connector side switch has passed from second to third position, and that the side switch wi er 76 is in engagement with the contact point 187 thereby7 placing the vertical line relay 68 in contro o the rlnger relay 82 in the same manner in which the rotary, magnet 71 came .under the control of .the vertical line relay when the side switch passed :from first to second position.

Therefore, when the vertical line `relay 68 operates, an energizin current flows through the ringer relay 82 rom ground Gr8 through the springs 188 and 189, private magnet springs 190 and 191, sideswitch wiper 76,

vcontact point 187, rin er relay 82, 'springs 192` and 193 (bearing 1n mindl that the .dif' ferential relay is energized) to the bat-` tery lead 181, thence through battery B to ground G. Each time that the vertical and rotary line relays 68 and 69 have been energized, as explained, the differential relay 80 is energized also, but?` this has played no part until now. `The-rin er relay upon energizing operates to-bri ge across the line of the called subscriber the ringer generator K.' A signaling current, is, therefore, sent from the ringer` generator to the substation ringer 194. =As soon as the operator ceases to press the spring 139 the rin r relay 82 becomes dener 'zed and the re ay assumes The operator, after completed the call and signaled the line, restores the key e to normal position, whereby `the lamp relay 104 becomes bridged across the'vtrunk conductors 92 and 93. As soon as the called subscriber removes his receiver. 195 from the switchiso vertical line conductor 20T, thence through' rent out over the trunk conductors 92 and 93, which current passes through .thelamp 'relay 104 aforesaid, whereby the said relay becomes energized .and moves its armature 178 from the contact point 1 77 to the contact point 213. This circuit through the relay 104 may be traced from ground Gr7 through the side switch wiper 77, relay springs 212 and 210, winding 214 of the differential relay 80, winding of the rotary relay 69, shaft wiper 39, side switch Wiper 42, trunk conductor 93, through the springs 143 and 145, conductor 215, springs 216 and 217 to the relay 104, to the vertical trunk line conductor 92, side switch wiper 41, shaft wiper 38, connector vertical line relay 68,

winding 217n of the relay 80 to the battery lead 181, thence through battery B to ground Gr'. in this circuit energizes, as previouslystatedI and attracts its armature 17 8, whereby the circuit through the supervisory lamp 95 is broken and the lamp goes out, indicating tu the operator that the called subscriber has answered. The two substations A and D are now connected and communication .may be carried on over the circuit shown bythe heavy lines iii-Figs. 1 and 2i -When the subscribers are through talking and restore the' receivers to vtheir respective switch-hooks the operator is given the disconnectsignai as follows.' When the receiver 2is restored to the switch-hook 3 the energizing circuit lthrough the relay 99 becomes broken at the switch-hook 3 and contact point 4.` The said relay denergizes and the armatures 166 and 167 return to engagement with the contact points' v168 and 169, respectively. The engagement of the armature 166 and contact point 168 closes a circuit through the supervisory lamp 96, said circuit extending from round G through the ring 163 of the jack and ring 162 of vthe plug c to the armature 166, contact point 168, springs 218 and 219, through the lamp 96 to the battery lead 114, and throu h battery to ground G. The display'ofg this lam indicates to the operator that the subscrlber at substation A has restored his receiver to the*switch hook. When the called subscriber at substation D restores' the receiver 195 to the switch-hook 196 the energizing circuit through the relay 81y is destroyed, which latter in turn, upon denergizing, destroys the circuit through the supervisory relay 104 at the cord circuit E, at which instant the armature 178 returns to engagement with the The relay 104 being included contact point 177, whereby the circuit, as previously traced, is again established through the supervisory lamp 95. The two lamps 95 i and 96, thus displayed simultaneously, indicate to the operator that both subscribers yhave restored their receivers to theirrespeca connection with some substation of the private` branch exchange. In that event the relay 104 does `not vdenergize, but maintains a circuit through the signal lamp 94 after the relay 99 denergizes'. This circuit extends from ground Gs through the armature 167, contact point 169 to the lampA 94, thence through the springs 220 and 221 to the contact point 213, armature 17 8 to the battery lead 114, and from battery B to ground G. The glowing of the lamp 94 indicates to the operator that the trunk line conductors 92 and 93 are in the possession of a subscriber who desires some connection at the private branch exchange. Accordingly the operator operates the key e so that the springs 220 and 221, and 222 and 223 disengage, and the springs 224 and 225, and 226 and 227 engage. This operation of the said key destroys` the circuit through the sign lamp 94 when the springs 220 and 221 disengage. This disengagement of the springs 222 and 223 at this time is without eiect, but the en gement of the springs 224 and 225 and tg: springs 226 and '227 bridges across the trunk'line conductors ythe 'operators set o. The o erator, upon learning that substation D, or example, is desired, throws the keye in the' opposite direction, whereby, when the springs 148 and `149 ent gage, an energizing circuit, is maintained through the re ease relays 105 and 106, said circuit extending from ground G10 through the springs 149 and 148, through the release relays 105 and 106 to the battery lead 114, thence through battery B to ground G. She then removes the plug cz'from the jack C and inserts the former in the jack C, as' shown in Fig. 1. When the ring 162 engages the ring 228 a circuit is established through thel signal lamp 96, extending from Aground G through the ring 228 `and rin 162,y armature 166, contact point 168, throug the springs 218 and 219, lampl 96 to the battery lead 114, thence throu battery B to round G. The o erator t en restores the ey 11' to norma position, whereby the springsy 220 and 221 again engage and es'- tablish the circuit through the signal lamp 94.. The key e is thenoperated to disengage the springs 157 and 154'from the springs 158 and 153, and to press the saidsprings into Contact with the springs230 and 229, re-

s ectively, whereby upon the engagement of t e springs 154, 229 and springs 157, 230

the ringer generator 97 becomes bridged across the line conductors 231 and 232 which lead io the substation D. VVhen'the key e returns to normal position the springs 157, 158 and 153, 154 again engage. YVhen the called subscriber at substation D answers, an energizing circuit is then established through the relay 99, which supplies the called substation D with battery current for talking purposes. This circuit extends from ground i through the winding 150 of the relay 99, springs 151 and 152, through the springs 153 and 154, sleeve 155 to the sleeve spring 233, conductor 232 to the substation primary winding 16, transmitter 18, through the springs 14 and 15 to the conductor 231, tip spring 234, tip of the plug 156, thence through the springs 157 and 158, key springs 160 and 159 to the Winding 161 of the coil 99, thence to the battery Vlead 114, and through battery B to ground G. The relay 99 energizes and operates, as explained, when the armature 166 disengages from the contact point 168. The circuit through the lamp 96 becomes broken, thus indicating that the subscriber at substation D has answered. Furthermore, when the armature 167 disengages from the contact point 169 the circuit through the signal lamp 94 is broken, and when the signal disappears from both lamps the operator knows that both subscribers are in possession of the line.4

After the conversation is finished and the receivers at the substations D and D are restored to their switch-hooks, a disconnect signal is given the operator when the lamps 95 and 96 are caused to glow simultaneously. When the subscriber at substation D5 restores his receiver the energizing circuit through the relay 104 becomes broken, and

"the lamp 96. Both o the subscribers having left the line, the operator then removes the plug c2 from the jack C, whereby, when the ring 228 of the jack C2 and the ring 1 62 of the plug c: disen age, the energizing circuits through the re ease relays 105 and 106 become broken. The said relays denergize,

lbut the relay 105 beinga quick-acting relay and the'relay 106 a slow-acting relay, the armatures 170 and 171 of the relay 105 engage the contact points 174 and 175 before the armatures 172 and 173 disengage from the ground post 176, and thus bothr trunk line conductors 92 and 93 aie grounded simultaneously. The grounding of conductors 92 and 93 at this time closes energizing circuits through the relays 68, 69 and S0.

The circuit through the relay 68 extends from ground G through the Contact' point 176, armature 172, contact point 17 4, armature 170, vertical trunk conductor 92, side switch wiper 41, contact point 54, shaft fwiper 38, relay 68, winding 217 of the relay to the battery lead 181. The energizing circuit through the. relay 69 extends from ground G11, armature 173, switch wiper 42,

contact point 55, shaft wiper 39, relay 69, f

ythrough the release relay 63 of the selector switch Hin series with the release magnet 73 `of the connector I. The current now in passing, as before stated, through the winding 214 aids the winding 2172l in maintaining the springs 193 and 192 in contact. The energizing circuit through the release relay 63 and the release magnet T3 extends from ground G12 at the selector H through the side switch wiper 43, release relay 63, shaft wiper 40, through thetrunkrelease springs 234a and 235, release magnet 73, springs 192 and 193 to the battery lead 181, thence through battery B to ground G. When the-connector release magnet 73 is thus supplied with current it is energized, and asa result the lswitch shaft and side switch are restored to normal position, thus breaking the connection between the connector switch shaft wipers y65, 66 and 67 and the normal conductors 183, 184 and 185. The back-release relay 63, being in the saine circuit with the release magnet 73, energizes simultaneously with the release magnet 73, and operates to close a circuit through the selector release magnet 62. When the ground to the line conductors 92 and 93 is interrupted all the magnets involved in the rclease are denergized and all the switches are fully restored. Suppose that the subscriber at substation D wishes a connection with some subscriber D of the central exchange. `In that event the subscriber at substation D removes his receiver from the switch-hook, whereby an energizing circuit is established through the line relay 235, which in turn operates to close a circuit through the line lamp 236. The operator, seeing the line signal, inserts the plug c into the jack C, and upon learning that an outside connection desired removes the said plug and inserts the trunk line plug c2 instead. She now throws the key e to operate the springs, as shown in Fig, 11 The subscriber at substation l) may now operate his calling device and es;- tablish his own connection independently of the operator. The calling subscriber at sub- The relays 68 station D suitably operates his calling device for each digit oiv the nui'nber 220; When the button 28 presses the 'spring 30 onto the ground post 34 an energizing circuit is established through the vertical line relay 58 vof I 'and `158, springs 160 and 161, through the relay 101, winding 237, through the springs 144 and 142 to the vertical line conductor 92, thence through the side switch wiper 41, vertical line relay 58, bridge-cut-off springs 179 and 180 tothebattery lead 181, thencethrough battery B to ground G. Then when the rotary button29 is pressed a rotary impulse pa'sses from the ground post 34 to the spring 3 1, rotary line conductor 232, sleeve spring 233 and sleeve 155, through the springs 154 and 153, sprin 152 andl 238, through the relay 102, win lng 239 of the relay 100, through the springs 145 and 143 to the rotary trunk line conductor 93, side switch 42, rotary line relay 60, bridgecut-ofi springs 182, 179 and 180 to the bat-` tery lead 181, thence through bat-tery B to ground G. Ity will be seen that these two circuits incluge the windings of the relays 100, 101 and 02. The said relays energize, but their operation at this time is without eiect. After the subscriber at substation D has operated the central office switches and established connection with substation #220 the called subscriber is then signaled, and

Y in response to the signal removes the receiver from .the switch-hook, which closes an energizin circuit through the relay 81, as previous y explained, which relay 1in turn operates to provide the calling line with battery current for talking purposes, as follows from ground G7 at the connector I through the springs 212 and 210 and winding 214, relay 69 to the trunkA line conductor 93, as before, through the springs 143 and 145, winding 239 of the diier'ential relay 100, rela 102, springs 238 and 152, springs 153 an 154, through'the jack C2 to the rotary line conductor 232, thence through the substation D to the vertical line conductor 231, and again through the jack C2 to the springs 157 and 158, through the springs 160 and 161", relay 101, winding 237 of the coil 100, springs 144 and 142 tothe vertical trunk line Aconductor 92, thence through the connector armatures, but at this time withouteifect.

The two substations and D are now connected, and comluumcation may be carried on over the circuit indicated by the heavy lines in Figs. 1 and 2. The release of the central olice switches occurs, as before, when the subscriber at substation D grounds both line conductors 231 and 232 simultaneouslythat is, the ground impulses delivered to the line conductors 231vand 232 simultaneously pass to the connector I, Aenergizing the line relays 68 and 69 and the di erential relay in the manner previously explained,

whereby the connector switch I together withA the first-selector lswitch H are .restored to normal condition. Also, at the same time, when the conductors 231V and 232 are grounded simultaneously, the windings 237 and 239 101-and 102 -maintain their armatures in an 1 attracted position, andv the armatures 240 and 241 of the differential relay 100 return to normal position, whereby a circuit is established through the relay 103. This cire cuit extends from ground G13 through the armature 242, contact point 243, contact point 244, armature 245, armature 241, contact point 246, through the winding 247 of the relay 103, thence to battery lead 114, and through battery B to ground G. The relay 103 becomes energized and attracts its armatures 248 and 249, whereb a locking circuit is closed through the win in 250 of the relay 103 and also through t e supervisory lamp 96. The locking circuit extends from ground G through the jack and lug to the contact point 251, armature 240, t rough the springs 222 and 223 to the armature 248, contact point 252, through `the winding 250 of the relay 103, thence to battery lead 114 and through battery B to ground G. The relay 103 isv thus maintained energized by this locking circuit when the first .circuit traced lthrough the winding 247 becomes broken, at

which time the ground is removed from the line conductors 232 and 231. As long as the relay 103 is energized the circuit from ground Gw through the armature ,249, contact point 253, springs 254 and 219, lamp 96 vto the battery lead 114, thence through battery B and to ground G is maintained, thus indicating to the operator that the subscriber at substation D is through with the trunk line. The o erator then removes the plug c2 from the )ack C2 and restores the key e to normal position. l When the plug c2 is removed from the 'ack C2 the locking circuit through the windlng 250 of the relay 103 becomeslbroken, and the 'said relay denergizes, cutting oli:` the ground connection from the su ervisory lamp'96.

t has been explained how a call leaves the rivate branch exchange, and it vwill now be assumed that a call comes in on the imanes trunk line conductors 92 and It is to be understood that the trunk line -that terminates in the cord circuit E has assigned l "fmatic ofiice who wishes a connection with the' ysub-exchange calls the numberv 230 yand rfindsfthe normal rdnductors'y 255, 256 and "12459." ow, when'the normal conductors 255 and v256r are seized `by a` connector switch, the energizing circuit 'for the back-bridge relay 81 of the connector, already described, is immediately established through the supervisory relay 104 at the cord circuit E. This circuit extends fromthe vertical winding of the back-bridge relay to the vertical trunk line conductor 92, through the relay 104, springs 217 and 216 of the key e, conductor V215, through the springs 145and 143 to the rotary trunk line conductor 93, thence through the back-bridge relay of the connector, as previously explained. The relay 104, being included in the circuit of the backbridge relay of the connector, becomes energized and attracts its armature 178 to engage with the contact point 213, whereby acircuit is closed through the signal lamp 94. The said -circuit extends from ground G8 through the armature 167, contact point 169, 'through the lamp 94, springs 220 and-221,

f contact point 213, armature 178 "to the-bat-l tery lead 114, thence through battery B to ground' G. The display or glowing of the said lamp indicates to the operator or attendant that the trunk line conductors 92 and 93 leading to the main central exchange have been seized, and that a submriber desires connection with some substation of the private branch exchange. The operator opcrates the key e so that the springs 220 and 221, 222 and 223 disengage and the Springs 224 and 225, and 226 and 227 engage.

- this operation of the key the circuit through `the lamp 94 becomes broken and the operators set 0 becomes bridged across the `trunk line conductors 92 and 93. The disengagement of the `springs 220 and 221 breaks the circuit through the signal Vlamp 94. The disengagement of the springs 222 and 223 at, this time is without effect. The engagement of the springs 224, 225 and 226, 227 bridges the operators set o across the trunk line conductors 92 and 93. The operator, upon learning that substation D, for example, is desired, inserts the plug c into the ]ack C2, which latter is allotted to theline leading to "the substation D. Immediately, ,l l.,.then, thering 162 of the plug c2 engages the rin f-228-ohf the jack'Cz, and a circuit is estab ished through the supervisory lam'p 96 over conducting paths explained. AThe' op'- erator now operates the key e to bridge-the ringer generator 97 across the lineconductors 231 and 232 to signal the subscriber at sub# station D. When the subscriber at substation D removes the receiver 8 from the switchhook y9V a circuit is closed through the relay 99, as previously explained. The Said relay` energizes and attracts its!` al'ratures 166 and 167. When the armature 166 disengages from the contact point 168 the circuit through the signallamp 96 isbroken,

,and the operator the-n knows that the subscriber at. substationl D has answered. When the subscriber at substation D re-` stores his' receiver to the switch-hook the energizing circuit through. the relay 99 is broken, and the armatures 166 and 167 engage the contact points168 and 169, thereby closing the circuit through the supervisory lamp 96 and the signal lamp 94. W hen the calling subscribery on the trunk conductors 92 and 93 releases the centraloiiice switches vthe circuit through the relay 104 becomes broken, whereby the relay denergizes and the armature 178 passes from the contact point 213 to the contact point 177, and the es r circuit through the `lamp 94 'is broken; and

a circuit is established through the signal lamp 95, whereby the operator is given the disconnect signal when both lamps 95 and 96 glow simultaneously. Suppose that after the subscriber at substation D had restored the receiver to 'the switch-hook the sub- Ascriber'on the" line conductors 92 and 93 desired a subscriber at substation A. In that event the relay 104 does not dener ize, but` It will be apparent that when one of the automatic subscribers calls the cord circuit E the bridge-cut-ofl relay 64 energizes as soon as the connector places ground on the private normal conductor 259. The object in thus energizing this bridge-cut-of relay 64 is so well known that it needs no further comment.

`The relay coils usedin the trunk circuit E may be wound to any suitable resistance, but goed results have been obtained when the relays 99, 105 and 106 are Wound to a resistance ofV one hundred ohms each; the relays 100, 101 and 102 to twenty-five ohms each; and the4 relays 103. and 104 to five hundred ohms each.

From the foregoing it will be seen 'that I provide an improved semi-automatic telephone trunking system in which the operator at the cord circuit of a two-way trunk is equipped with supervisory apparatus for supervisingV any and all connections made through the medium ofthe trunk line and the cord circuit. Such operator is also equipped .with means for extending connections in either directionthat is to say, for

either receiving or sending calls over the trunk line, as Well as for releasin both manual and automatic connections a ter the' subscribers arethrough talking. An auto-` matic private exchange subscriber, desiring -to lcommunicate with a subscriber at the main exchange, first gets the attention of the operator, and is then given a trunk line connection to the main exchange. lThis having been doneftl calling subscriber can then Atransmit the call and operate the automatic Y cord circuit connection with the trunk line connection thus established. In either case the operator has complete supervision of the established connection, and is also provided with means for releasingany andall switches or otherl devices after the subscribers are through talking. Moreover, it will be seen,

that telephone service is thus provided between common battery manual subscribers and common battery automaticsubscribers. f

With this arrangement one or more of the subscribers of the manual exchange can be accorded special privileges, so to speakthat is to say, can be given special automatic service to a main or automatic exchange. This is sometimes desirable, and with my invention one or more of the telephones at the manual exchange can be equipped `for transf mitting the electrical impulses necessary for operatlng the automatic switches of an automatic exchange. Such connections, however, as explained, are subject to the manual supervision of an operator. Furthermore, any subscriber at the automatic exchange can call the trunk line and then, through'the medium of the trnkin y operator, obtain connection vwith any su scriber of the manual exchange, c

What I claim as my invention is:- v

1. In a telephone system, an automatic main exchange, a privatebranch exchange for manual subscribers, a trunk line connectingf the main exchange with the branch exchange and terminating at the main exchange in automatic switching apparatus,

When a manual private exand at the branch exchange in a cord circuit, said cord circuit comprising means whereby an automatic subscriber may be placed in connection with the trunk line and then permitted to complete the call automatically, and means whereby if one of the manual subscribers wants a connection to the main exchange the operator completes the connection automatically and then places the calling subscriber in connection with the trunk line signals controlled from all of said subscribers lines, and a common source of energy for operating all of said signals'and for supplying talking current to all of said mes.

2. In a telephone system, a main exchange, a private branch exchange, manual and automatic subscribers lines allotted to the private branch exchange, a trunk line connecting the main exchange with the private branch exchange, a terminal for said trunk line, automatic subscribers line signals and manual subscribers linev signals a cord circuit having an automatic calling evice whereby if a manual subscriber wants to make a call to the main exchange the operator completes the callV automatically over said trunk line, each automatic subscriber at the branch exchange being also provided with an automatic calling `device whereby if he wants to make a call to the main exchange yhe may be placed in connection with the trunk lineand then permitted to'make vhis own call, said cord circuit also adapted, if a subscriber in the main exchange wants to call a subscriber in the\ branch exchange, to be called automatically by the calling subscriber of the main exchange, whereby the operator may then con nect the callin main exchange subscriber with any one o the private branch exchange subscribers, signals controlled from all of said subscribers lines, and a common source yof energy for operating all of said Asignals and for supplying talking current to all of said'lines.

3. .In a telephone system, a callinglsubexchange automatic subscribers line and a called main exchange automatic subscribers line, means including a manual cord circuit whereby the calling subscriber ma estab lish connectionA with the called su scriber, said cord circuit ycomprising supervisory means includin a lampl whereby, when the automatic calhng subscriber releases the established connection, the supervisory lamp is displayed, and whereby if the'callin subscriber starts to make another call efore the cord circuit is taken down the lamp is retired.

4. In a telephone system, a cord circuit one end of which -terminates in a trunk line and the other end in a plug, a front supervisory lamp, a back .supervisory lamp, a trunk supervisory lamp, means comprising Vso Lavande a key whereby an automatic subscriber may be connected with the trunk line and may then make his own call, means comprising a calling device whereby,if a manual subscriber wants to make a call, the operator may vcomplete the call automatically, other 'means whereby another subscriber ma i manual subscriber calls, to be displayed when said manual subscriber hangs up his receiver, and to be retired if the said manual subscriber again removes his receiver, said back supervisory lamp being adapted when either the automatic or manual subscribers call to be retired when the called subscriber answers, and to be displayed again when the called subscriber `hangs-up,

said trunk supervisory lamp adapted to be displayed'whenthe aforesaid automatic calling subscriber finds the trunk line, and to be retired when the called subscriber answers.

5. In a telephone system,

a private branch exchange comprising a manual subscriber station A and an automatic subscrlber station D and a cord circuit E, a main automatlc exchange, a trunk line connecting said cord circuit E with said autoi matic exchange, subscribers lines allotted to said automatic exchange, said automatic exchange comprising automatic apparatus by means of which one line may automatically be `put in connection with another, means whereby either the automatic or manual sub- Scribers D or A may, through the cord circuit' E, be put in connection with any of the automatic subscribers of the main exchange, the automatic subscriber D being provided with means whereby after a connection is once established wlth one of said main exchange subscribers the connection may then be automatically broken by the calling subscriber, and releasing means allotted tothe trunk line wherebytheI operator at the cord circuit E may release the automatic apparatus, signals controlled from all of said subscribers lines, and a common source of energy for operating all' of said signals and f or supplying talking current to all of said mes. y

6. InV a telephone system, an automatic switch, a calling substation suitably connected withsaid switch, condensers inr the circuit between the substation and` the switch, and means for manuallyclosingconnectons around said condensers to permit the calling subscriber to operate said switch, a"'signal controlled from said substation, and a common source of energy for operating said signal and for supplying talking current to said substation.

7. In a telephone system, a calling substation including a calling device, an automatic switch, a circuit connecting said switch with said calling' device, condensers in said circuit, and means for closing connections around said condensers to permit the calling impulses to pass to the auto` matic switch, a signal controlled from said substation, and a common source of-energy for operating said signal and for supplying talking current to said substation.

8. In atelephone system, a cord circuit, condensers in the talking strands of said circuit, a centralized source of talking current, and means for establishing shunt connections around each of saidcondensers -to permit talking current to pass entirely through 'said shunt to the calling subscriber. 9. In a telephone system, an automatic switch, a trunk line leading the-reto, a 'cord circuit'at the other end of said trunk line, a telephone line, a key switch for operatively connecting the cord circuit with the trun line to permit the calling subscriber to operate said automatic switch, calling and called supervisory signals for indicating to the operator when a disconnection is desired, and a. common battery for supplying talking and operating current.

10. In a telephone system, an automatic switch, a trunk line leading thereto, a trunking operators cord circuit for the other end cfs-aid trunk line, condensers in said cord circuit, a telephone line connected with the cord circuit, means for closing parallel connections around said condensers to permit the calling subscriber to operate said automatic switch, suitable inductive resistance in said parallel connections, a signal controlled from said telephone line, and a common source of energy for operating said signal and for supplying talking current to said line, l

1l. In a telephone system, a trunk line, a trunking operators cord circuit connected with said trunk line, condensers in said cord circuit, an automatic switch, a. calling tele-`- phone line connected with said cord circuit, an operators key ,switch provided with means for closing connections around said condensers` means at the calling substation for transmitting electrical impulses over the telephone a line and lsaid connections and trunk line to operate said automatic switch, and suitable instrumentalities for supplying talking current over the trunk line to a calling subscriber,

12. In a telephone system, anautomaticswitch, a. trunk line leading thereto, a cord circuit at the other end of said trunk line,

a telephone line, a key switch for opera tively connecting the cord circuit with the trunk line to permit the calling subscriber to operate said automatic switch, and suitable instrumentalities for supplyin talking current over the trunk line to a cal ing subscriber.

13. In a telephone system, an` automatic switch, a trunk line leading thereto, a trunking operators cord circuit for the other end of said trunk line, condensers in said cord circuit, a tele-phone line connected with the cord circuit, means for closing parallel connections around said condensers to permit the calling subscriber to operate said automatic switch, suitable inductive resistalice in said parallel connections, and suitable instrumgntalities for supplying talking current over the trunk line to a calling subscriber. i

14. In a telephone system, an automatic switch, a trunk line leading thereto, a cord circuit for the other end of said trunk line, a key switch controlling the connection between the cord circuit and the trunk line, an operators calling device for operating said automatic switch, said calling device adapted to be connected with the trunk line by the actuation of said key switch, and suitable instrumentalities .for supplying talking current over the trunk line to a calling subscriber.

15. In a telephone system, an automatic switch, a trunk line leading thereto, atrunking operators cord circuit provided with \means for calling over th'e trunk line 4to operate said automatic switch, condensers in said cord circuit, a telephone line, means controlled by the operator for connecting the telephone line around the said condensers to permit the subscriber of said line v to operate the said automatic switch over the trunk line, and suitable instrumentalities for supplyin talking current over the trunk line to a ca ling subscriber.

16. In a telephone system, an exchange comprising manual switchboard ap aratus, subscribers lines terminating at said manual switchboard apparatus, one. or more of said lines vbeing provided with means for transmittin impulses suitable for calling automatical y, another exchange com rising automatic yswitches and subscribers `vlines provided with means for calling automatically, a trunking operators cord circuit, a

trunk line for connecting the first-mentioned. exchange with the last-mentioned exchange, a trunking operators calling mechanism for calling automatically over the trunk line to operate the switches at the last-'mentioned exchange, means by which the trunking operator connects a-telephone line with the trunk line to permit the callin subscriber to control the said automatic switches, and suitable instrumentalities for cuit.

cuit, an operators key `switch provided with means for closing connections around said condensers, means at the calling substation for transmitting electrical impulses over the telephone line and said connections Aand,

trunk line to operate said automatic switch, and front and back supervisory signals for said cord circuit.

18. In a telephone system, a cord circuit, condensers in said. circuit, a centralized source of talking current, means for estab,- lishing connections aroundeach of said condensers to permit talking current .to pass` entirely through said shunt to the Ycalling subscriber, and front and back supervisory signals for said cor'd circuit. n

19. In a telephone system, an automatic switch, a trunk line leadin thereto, a cord circuit at the other end o said trunk line, a telephone line, means including a key switch for operatively connecting the cordA circuit with the trunk line and for permitting `the calling subscriber to operate said automatic switch, and front and back super' visory-signals for said cord circuit.

20. In a telephone system, an automatic switch, atrunk line leading thereto, a trunking operators cord circuit for the other end of said trunk line, condensers in said cordi. circuit, a telephone line connected with the cord circuit, means for closing parallel connections around said condensers to .ermit the calling subscriber to operate sai automatic switch, suitable inductive resistance in said parallel connections, and front and back ysupervisory signals for said cord cir- 21. In a telephone stem, an automatic switch,l a trunk line lea ing thereto, a trunk ing -operators cord circuit provided 'with means for calling over the trunk. line to operate said automatic switch, condensers in said cord circuit, a telephone line, vmeans controlled by the operator for connecting the telephone line around the said condensers to permit the subscriber of said line to operate the said switch over the trunk line, and front` and back 'supervisory'signals for said cord circuit.

22. In a telephone system, an exchange comprising manual switchboard apparatus, subscribers lines terminating at said manual switchboard apparatus, one or more of'sa'id lines being provided with means for transist mittinv impulses suitable for calling automatica 1y, another exchange comprising auisc Va trunking operators cord circuit, a trunk line for connecting the first-mentioned exchange withV the last-mentioned exchange, a

trunking operatorscalling mechanism for calling automatically over the trunk line to operate the switchesat the last-mentioned exchange, means by which the trunking operator connects a telephone line with the trunk line to permit the calling subscriber to control the said automatic switches, and front and back supervisory signals for said cord circuit.

23. In a telephone system, a trunk line,.

`and supervisory relay mechanism for said cord circuit, said mechanism comprising front and backV supervisory rela. s, as set forth, and means .for supplying ta king cur- 4rent over the trunk line to the i station.

24. In atelephon system,a cord circuit, i condensers in the talking` strands of said said shunt .to, the calling calling subcircuit, al centralized source of talking current,` means for establishing shunt connections around each of said condensers to permit talking current to pass entirely through subscriber, and supervisory relay mechanism for said cord circuit, said mechanism comprising front and back supervisory relays, as set forth.

25. In a telephone system, an automatic, switch, a `trunk line leading thereto, a cord circuit at the other 'end of said trunk line, a telephone line, means including a ke .switch for operativel connecting the cor circuit with lthe trun line and for permitting the y calling subscriber to operate said automatic switch, supervisory relay mechanism comprising front and back supervisory relays, las set forth, and means for supplying talking current over the trunk line to said lline. 26. In a tele hone s stem, an automatic switch, a trunk ine lea ing thereto, a trunk- Y ing operators cord circuit provided with means forl calling over the trunk line to `operate said automatic switch, condensers in said cord circuit, a telephone line, .means controlled by the operator for connecting the telephone line around the said condensersfto permit the subscriber of said line to operate the said automatic switch oyer the trunk line, supervisory rela mechanism for said cord circuit, said mec anism comprising` :front and back supervisory relays, as setaforth, and means for supplying talking current over the trunk line to said line.

`cf Y li, c to permit the calling subscriber to oper- 27. Iny a telephone system, an exchange I comprising manual switchboard apparatus,

subscribers lines terminating at said manual switchboard apparatus, one or more of said lines being provided with means for transmitting, impulses suitableA for calling auto! and back supervisory relays, as set forth, and means for supplying talking current over the trunk line to saidline.

28. In a telephone system, a trunk line, a trunking operators cord circuit connected with said trunk line, condensers in said cord circuit, an automatic switch, a calling telephone line connecting with said cord circuit, an operators key switch provided with means for closing connections around said condensers, means at the calling substation for transmitting electrical impulses over the Atelephone .line and said connections and trunk line to operate said automatic switch, and supervisory relay `mechanism for said cord circuit, said mechanism comprising a relay provided with a winding having end and intermediate terminals, and a battery normally disconnected from the end terminals of said relay, but permanently conneted with the intermediate terminal thereof.

'29. In a telephone system, a cord circuit, condensers in said circuit, a centralized source of talking current, means for establishiiig connections around said condenseis to permit talking current to pass to the calling subscriber, and supervisoryrelay mech'- anism for said cord circuit,- saidlmechanisin comprising a relay provided with a windin having end and intermediate. terminals, an a battery normally disconnected from the circuit, said mechanismV comprising front` ion end terminals of said relay, but permanentlyV connected with the intermediate terminal thereof. Y

30. In a telephone system," an automatic Switch, a trunk line leading thereto, a cord circuit atthe other end of said trunkline, a telephone line, a key switch for operatively @iecting the cord-circuit withl the trunk ate said automatic switch, and supervisory relay mechanism for said cord circuit, said mechanism comprisingI a' relay provided with ing operators cord circuit for the Other end a winding having end and intermediate ter-VA cally, a trunking operators cord circuit, a

minals, and a battery normally disconnected trunk line for connecting the first-mentioned from the end terminals of said relay, but exchange with the last-mentioned exchange,

Pellllnently CODDBCGd .With the intelma trunkng operators calling mechanism for diate terminal thereof. l calling automatically over the trunk line to 31. In a telephone system, an automatic operate the switches at the last-mentioned switch, a trunk line leading thereto, a trunkexchange, means by'which the trunking operator connects a telephone line 'with the of said trunk line, condensers in said cord trunk line'to permit the calling subscriber circuit, a telephone line connected with the to control the said automatic switches, and cord circuit, means for'closing parallel con# supervisory relay mechanism forsaid ,cord nections 'around said condensers to ermit circuit, said mechanism comprising a relayA the calling subscriber to operate sai auto` provided with a winding having end and inmatic switch, suitable inductive resistance termediate terminals, and a battery non in said parallel connections, and supervisory mally disconnected from the end terminals relay mechanism for said cord`circuit, 'said 'of said relay, but permanently connected mechanism comprisin arelay provided with with the intermediate terminal thereof. a Winding having en and intermediate ter- 35. A semi-automatic telephone exchange minals, anda battery normally disconnected trunking system provided with selectors,and from the end'terminals of said relay, but connectors responsive to a calling subscriber, permanently connected with the intermedimeans by which an operator connects a selecate terminal thereof. ,A n tor with the line ofthe calling subscriber be-A 32. In a telephoney system, an automatic fore the call can be extended in the direction switch, a trunk line leading thereto, a cord of the called subscriber, calling and called circuit for the other end of said trunk line, a supervisory signals for indicating to the opkey switch controlling the connection be-` erator when a disconnection is desired, and tween the cord circuit and the trunk line, an a common battery for supplying talking and operators. calling device for operatin said operating'current. f v automatic switch, said callingv device a apted 36. In a telephone exchange system, a pluto be connected vwith the trunk line by the Irality of-subscribers lines, a number of first actuation of said key switch, and supervisory selectorl switches less .than the number of rela mechanism for said cord circuit, saidk subscribers lines,- means manually controlled mec anism comprisin a relay provided with for bringing said first selector switches into a winding having en and` intermediate terconnection with calling lines, together with minals, anda battery normally disconnected means whereby the said selector -switches from the end terminalsxof said relay, but maythen be controlled bythe subscribers to permanently connected with the intermedi- "selec-t theu lines Wanted, and to restore the ate terminal thereof. f switches a'fter use, calling .and called super- 33. In a telephone system, an automatic visory devices connected with theinanual switch, a trunk line leading thereto, a trunk-`A `portion of the apparatus to .indicate to the ing operators cord circuit' provided with). operators the necessity fora disconnection -means for calling over the trunk line to opand a commonvbattery' for supplying talking erate said automatic switch,zcondensers in and operating current.V

said cord circuit', av telephone line, meansv 37. In a telephone exchange system, a plucontrolled by `the operator for connecting rality of subscribers lines, a number of rst the telephone line around the said condens- Selector switches less than the number of ers to permit the'subscriber of said line toA subscribers lines, operators cord-circuits Operate the said automatic switch over the 'for connecting said first *selector switches trunk line, rand supervisory relay mechanism with the calling lines, together with. sending -for said cord circuit, said mechanism compris-v devices, at the substationsgfand responsive ing a relay providedwith a Winding having devices at the central station whereby the end and intermediate terminals. and abat- Y tery .normally disconnected from lthe end trolled bythe subscribers t'o select the lines terminals of Said relay, but permanently Wanted, and to. restore the switches after connected with the intermediate terminal use, line-annunciators and calling and called thereof. clearing-out annunciators connected with the 34. In a telephone system, an exchange lines and cords, res ectively, to indicate to comprising manual switchboard apparatus, the operators the desire of the respective subscribers lines terminating at said mann impulses lsuitable Ifor calling 38. In atelephone exchange stem, a pluautomatical y, another exchange comprising rality ofsubscribers lines terminating upon automatic switches and subscribers lines sprin jacks, a line signal associated with provided with means for calling automatieach Jack and controlled from the subscrib- ,said selector switches may vtlien be con- Aion subscribers for connection and Adisconne'cual switchboard'apparatus, one or more of tion, and a common" battery for supplying aid lins being ypro/vided with` means for talking and operatingcurrent. v

ransmi 1n ers station, a plurality of first selector y switches less in number than the number of lines, operators4 connective circuits with answering plugs and means to connect a call ing line therethrough with an idle first se lector switch, a clearing-out signal associated after a connection is manually initiated in response to a call, the calling subscriber ma thereafter complete the connection throug the automatic switches and at the end of the conversation. may restore the same, and a common battery for supplying talking and operating current. l

39. In a telephone system, a trunk line, a

trunking operators cord circuit connected with said trunk line, condensers in said cord circuit, an automatic switch, a calling telephone line connected with said cord circuit,

an operators key switch provided with,

means for closing connections around 'said condensers, means at the calling substation for transmitting electrical impulses over the telephone line and said connections and trunk line tooperate said automatic switch, suitable instrumentalities for supplying talking current over the trunk line tov'a. calling subscriber, and means for automatically supplying current for ringing purposes.

40. In a telephone system, an automatic switch, a`trunk line leading thereto, a cord circuit at the other end of said trunk line, a

telephone line, a key switch for operatively connecting the cord circuit with the trunk line to ermikt the calling subscriber to operate sald automatic switch, suitable instrumentalities for supplying talking current over the trunk line to a calling subscriber,

and means for automatically supplying current for ringing purposes.

`41. In a telephone s stem, an automatic switch, a trunk line lea ing thereto, a trunking operators cord circuit for the other end of sald trunk line, condensers in said cord circuit, a telephone line connected with the cord circuit, means for closing parallel con-s nections around said. condensers to permit the calling subscriber to operate said automatic switch, suitable inductive resistance in said parallel connections, suitable instrumentalities for supplying talking' current over the trunk line to a calling subscriber, and means for automatically supplying cur rent for ringing purposes.

42. In a telephone system, an automatic switch, a trunk line leading thereto, a cord circuit for the other end of said trunk line, a key switch controlling the connection between the cord circuit and the trunk line, an operators calling device for operating said automatic switch, said calling device adapted to be connected `with the trunk line by the actuation of said key switch, suitable instrumentalities for supplying talking current over the trunk line to a calling subscriber, and means for automatically supplying current for ringing purposes.

` 43. In a telephone4 system, an automatic switch, a trunk line leading thereto, a trunking talking current lover the `trunk line to a calling subscriber, and means for automati` cally supplying current for ringing purposes.

44. In a` telephone system, an exchange comprising manual switchboard apparatus, subscribers lines terminating at said manual switchboard apparatus,'one or more of said lines being provided with means for transmitting impulses suitable for callin automatically, another exchange comprising automatic switches and subscribers lines provided with means for calling automatically, a trunking operators cord circuit, a trunk line for connecting the first-mentioned xchange with the last-mentioned exchange, a trunking operators calling mechanism for calling automatically over the trunk line to operate the switches at the last-mentioned exchange, means bywhieh the trunking o erator connects a tele hone line with t e trunk line to permit tlie calling subscriber io control the said automatic switches, suitable instrumentalities for supplyin talking current over the". trunk line to a calling subscriber, and lmeans for automatically supplying current for ringing purposes.

45.- In a telephone system, a trunk line,`a trunking operators cord circuit ,connected `with saidtrunk line, condensers insaid cord circuit, an automatic switch,a calling telephone line connected with said cord circuit, an operators key switch provided with means for closing connections around said condensers, means at the calling'substation for transmitting electrical impulses over the telephone line and said connections and trunk line to operate said automatic switch, front and back supervisory signals for said cord circuit, and means for automatically supplying current for ringing purposes.

46. In a telephone system, a cord circuit, condensers in said circuit, a centralized source of talking current, means for establishing connections aroundeach of said condensers to permit talking currentto pass entirely through said shunt to the calling subscribers, front and back supervisor signals for said cord circuit, and means or automatically supplying current for ringing purposes.

6 47. In a telephone system, an automatic switch, a trunk line leading thereto, a cord circuit at the other end of said trunk line, a telephone line, means including a keyr switch for operativel connecting the cord circuit 10 with the trunk, line and for permitting the calling'subscriber to operate said automatic switch, front and back supervisory signals for said cord circuit, and means for automatically supplying `current for ringing 1 5 purposes.

48. In a telephone system, an automatic switch, a trunk line leading thereto, a trunking operators cord circuit for the other end of said trunk line, condensers in said cord circuit, a telephone .line connected with the cord circuit, means for closing parallel connections around said condensers to permit the calling subscriber tol operate said automatic switch, suitable inductive resistance in said parallel connections, front and back supervisory signals for said cord circuit, and means for automatically supplying current for ringing purposes.

49. In a telephone system, an automatic switch, a trunk line leading thereto, a trunking operators cord circuit provided with m'eans for calling over the trunk line to operate said automatic switch, condensers in said cord circuit, a telephone line, means controlled byfthe operator for connecting the telephone line around the said condensers to permit the subscriber of said line to operate the said vswitch over the /trunk line, front and back supervisory signals for' said cord circuit, and means for automatically supplying current for ringing purposes. I f

50. In a telephone system, an exchange comprising manual switchboard apparatus, subscribers lines terminating Aat said manual switchboard apparatus, one or more of said lines being provided with meansl for transmitting impulses suitable .for calling automatically, another exchange comprisingx automatic switches and subscribers lines provided `with means for calling .automatically, a trunking operators cord circuit, a trunk line for connectingthe first-mentioned exchange with the last-mentioned exchange,

a trunking operators calling mechanism for calling automatically over the trunk lme to operate the switches at the last-mentioned exchange, means by which the trunking operator connects a telephone line with the .trunk line to permit the calling subscriber tocontrol the said automatic switches, front and back supervisory signals for said cord circuit, and means for automatically supplying current for ringing purposes. 6l 51. In ar telephone system, means includextending a connection to a calle` line, an

operators position through which the connection extends, supervisory signals at said position under the control, respectively, of the calling and called subscribers, and suitable means for supplying talking current from a central source to the connected lines.

53. In atelephone system, means including a plurality of serially related automatic switches controllable over a calling line for extending a connection to a called line, an operator s position through which the connection extends, supervisory signals at said position under ythe control, respectively, of the calling and lcalled subscribers, operator controlled means for releasing said switches, and suitable'means for supplying talking current from a central source to the connected lines. l

54. In a telephone system, a trunk line,- manual equipment for extending connections to or from said trunk line at one end,

' automatic equipment comprising 'a pair of 100 line for connecting a calling line thereto, a

lcall signal and manual connective apparatus at the other end of said trunk line for y receivin the call and for extending the same to a cal ed line,.said manual a paratus also adapted to connect a second cal ing line with said trunk line, a second automatic switch associated with-said first switch and controllable over said trunk line to extendthe 120- said second calling line to -a second called line, a central source of current, and suitable means for supplying connected calling and called lines with talking current from said source. v

56. In a telephone system, a trunk line, manual equipment for extending connections to orl from said trunk 'line at one end, and automatic equipment comprising a pair of automatic switches one of which is controllable over the said trunk line for extending connections to or from said trunk line at the other end, whereby calling and called lines may be connected, and a circuit closed when one of said switches is operated for rendering the said trunk line busy to the other of said switches, a central sourceof adapted to connect la second calling line with said trunk line, a second automatic switch associated with said {irst switch and controllable over said trunkline to extend the said second calling line to a second called line, and a circuit closed when the said second switch is operated for rendering the said trunk line busy to `the said first switch, a central source of current, and suitf able means for supplying connected calling and called lines with talking current from said source.`

58. In a telephone system, a trunk line, manual equipment for extending connections to or from said trunk line at one end, automatic equipment comprising a pair of automatic switches one of which 1s controllable over the said trunk line for extending connections to or from said trunk line at the other end, whereby calling and called lines may be connected, means for rendering one of said switches inoperative whenever a. connection is extended to the said trunk line by means of the other switch, a central source of current, and suitable means for supplying connected calling and called lines wit talking current from said source.

59. In a telephone system, a trunk line, an

automatic switch at one end of said trunk` line for connecting a calling line thereto, a

call signal and manual connective apparatus at the other end of said trunk line `for receiving thel call and for extending the same toa called line,`saidmanua1 a paratus` also adapted to connect a second call1 said trunk line, a second automatic switch associated with said first switch and controllable over said trunk line to extend the said second calling line to a second called line, a relay for rendering said second switch inoperative controlled. by the said first switch, a central source of current, and suitable means for supplying connected calling and called lines with talking current from said source.

60. In a telephone system, a trunk line, means including an automatic switch for seizing said `trunk line at one end and a manual connective terminal and acall signal at-the other end for completing a connection over the said trunk line in one direction, means including the said manual uconnective terminal and a second automatic switch at the other end controllable over said trunk ing line withl 4 line for completing a connection over said v trunk line in the opposite direction, each connection when completed including a calling and a called subscribers line, a central 

